A cell-penetrating peptide (CPP), which is a peptide having a property capable of penetrating a cell membrane, usually includes 30 amino acids or less, and is known to have a property of freely passing through a lipid bilayer membrane. The CPP is also referred to as protein-transduction domains (PTDs) and membrane-translocating sequences (MTSs), and may pass through the cell membrane in a form of being coupled to an object to be delivered or being mixed therewith, thus to transport the object to be delivered such as a protein, DNA, RNA, or the like into a cell, as well as into cytoplasm, an intracellular organelle, or a nucleus.
The cell membrane of higher animals consists of a phospholipid bilayer. Due to the lipid bilayers being hydrophobic, it is almost impossible for most of the peptides, proteins, nucleotides, liposomes, and the like to migrate into the cell. Accordingly, the cell membrane may act as an obstacle in the process of migrating the peptides, proteins, a drug formulation of compound, or a gene therapy agent into the cell. To overcome this problem, migration methods using a cationic lipid, polyethyleneimine (PEI), a viral vector, or electroporation have been widely used in the art.
However, these methods have a limit to use due to a low cell penetration efficiency, limitation in applicable cell types, intracellular toxicity and the like. In order to overcome these limitations, using the cell-penetrating peptides has been widely attempted in recent years.
The CPP is an oligopeptide that has properties capable of reacting with the cell membrane to cause endocytosis or directly penetrate the cell membrane, and electrochemical and physicochemical properties capable of penetrating the cell membrane.
The CPP is a part of a translocator protein, and a representative example thereof may include a membrane translocating sequence (MTS) which is a hydrophobic region present in a signal sequence of human fibroblast growth factor 4, and Tat-PTD (basic amino acid domain) of a Tat protein which is one of viral proteins of human immunodeficiency virus (HIV).
In addition, many CPPs have been reported and have been commercialized up to now. However, most of the CPPs have a low degree of transporting materials into the cell by passing through the cell membrane due to their cell-specific properties, and effects thereof are also not high. In particular, in an environment including serum or sera, the penetration efficiency of passing through the cell membrane is reduced by about half as compared to the environment without the serum. Therefore, in order to transport a functional protein, DNA, or RNA into the cell, a development of CPP that has no cell-specific properties while having a high penetration efficiency even in the presence of serum is still required.
Advantages obtained by developing a novel CPP are that various types of regulatory materials necessary for cell differentiation, cell characteristic maintenance, or function regulation of tissue and organs can be efficiently introduced into the cell. In particular, the CPP is a very useful medium that can easily migrate proteins having a very limited active period into the cell, thereby achieving the desired purpose without any expected risk. On the other hand, the CPP has advantages of being capable of transfecting the object into the cell in a recombinant form or a form mixed with the subject. Such a possibility is primarily theoretical, but has been proven in some experiments. However, as described above, due to the limitations of existing CPPs, there is still a problem entailed in the cell penetration efficiency. Briefly, due to their cell-specific properties, the existing CPPs have different migration efficiencies for the materials, and a lower delivery efficiency than other media used in gene modification. At this point, works have been actively performed to find a delivery medium that can overcome the problems entailed in the existing CPPS and have no side effect.
Therefore, it is very important to secure candidates that have excellent cell penetration efficiency and cell permeability as compared with the cell-penetrating peptides known in the art, applicability as a fusion protein, and an exclusive technical superiority over amino acid sequences thereof.
The present inventor has searched for a novel CPP in order to find a delivery medium capable of efficiently delivering various types of regulatory materials necessary for cell differentiation, cell characteristic maintenance, or function regulation of tissue and organs, and has confirmed that the problems having the conventional media can be overcome by the novel CPP, then completed the present invention based on the finding.